1. Field of the Invention
The present invention relates generally to a non-volatile memory device and an associated fabrication method. Particularly, the invention relates to a non-volatile memory device that incorporates a series of either single memory cells or double memory cells having memory elements comprising a bi-stable layer with programmable electrical resistance sandwiched between two conductive layers. Additionally, the invention relates to a method for manufacturing the non-volatile memory device that incorporates a process for simultaneously conditioning the transition metal oxide layers of each memory cell in a series such that the transition metal oxide layers exhibit a bi-stable electrical resistance.
2. Description of the Related Art
Flash erasable programmable read only memory (FEPROM or flash memory) is used in semiconductor devices and provides for rapid block erase operations. Flash memory generally requires only the use of one transistor per memory cell versus the two transistors per memory cell required for conventional electrically erasable programmable read only memory (EEPROM). Thus, flash memory takes up less space on a semiconductor device and is less expensive to produce. However, the need to develop further space saving components and to remain cost efficient in the fabrication of semiconductor devices continues. To that end, the use of materials with programmable electrical resistance for semiconductor device applications has been studied. The electrical resistance of resistance-switching materials, including but not limited to transition metal oxide materials, can be changed significantly by external influences, including temperature, magnetic fields and electric fields. Electrical impulses applied to theses materials can “program” them, such that they exhibit a desired resistive property. Specifically, the following referenced articles, international application and U.S. Patent, all of which are hereby expressly incorporated by reference into the present invention for purposes including, but not limited to, indicating the background of the present invention and illustrating the state of the art, describe materials and classes of materials with programmable electrical resistance and simple electrical resistor devices made from these materials: “Reproducible switching effect in thin oxide films for memory applications” (A. Beck et al., Applied Physics Letters, Vol. 77, No. 1, July 2000); “Current-driven insulator-conductor transition and non-volatile memory in chromium-doped SrTiO3 single crystals” (Y. Watanabe et al., Applied Physics Letters, Vol. 78, No. 23, June 2001); “Electrical current distribution across a metal-insulator-metal structure during bi-stable switching” (C. Rossel et al., Journal of Applied Physics, Vol. 90, No. 6, September 2001); International Application Pub. No. WO 00/49659 A1; and, U.S. Pat. No. 6,204,139 issued to Liu et al. on Mar. 20, 2001. Transition metal oxide materials are one class of materials that can be conditioned such that they exhibit a bi-stable electrical resistance and, therefore, they have a wide range of potential applications. One possible use for such materials with programmable electrical resistance is in the memory cells of non-volatile memory devices. The present invention provides an improved non-volatile memory device and an improved method for fabricating the non-volatile memory device.